The present invention applies to the art of securing insulation to the walls of furnaces, kilns, soaking pits and the like and, more particularly, to securing a combination insulation blanket and modular block insulation to the inner walls of such structures.
Several years ago, the predominant method of insulating such heating apparatus as furnaces, incinerators and other devices of that nature was to use the heretofore conventional and well-known firebrick. The process of bricking the heated areas was expensive from a labor standpoint and extremely time consuming. Additionally, repair and replacement of the brick lining in such structures was both expensive and time consuming.
More recent developments in the art of insulating furnaces and such structures in the utilization of insulating blankets formed of ceramic materials or ceramic glass such as alumina. These blankets come in varying thicknesses from 1 to 3 inches and are formed into rolls of varying widths.
During the insulating process, the blankets are applied to the walls of the structure in layers of anywhere from 1 to 3 layers and often in a crisscross pattern. The blankets may be secured to the walls of the furnace or other structure in a number of different ways.
In nearly all heating devices such as furnaces and the like, the wall to which the blankets are supported is a metallic wall known as the cold wall. One manner of securing the blankets to the cold wall is the utilization of a threaded fastener which employs a drill point and self tapping combination on the end of the fastener. The fastener is drilled and threaded into the wall and projects outward from the wall. A number of these fasteners are spaced along the wall and blankets impaled upon the fasteners. Thereafter, a washer and nut are applied to the threaded fastener to pull the blanket down into secured position.
Another device which is used for smaller blankets is a pin which has a large washer secured on the end of the pin. The pin is pushed through the blanket and against the metallic cold wall and stud welded in place to secure the blanket.
A third device in prevalent use is a stud and washer combination wherein the stud includes a plurality of tapered notches. The studs are welded to the cold wall in a given array or fashion and the blanket impaled upon the studs. Thereafter, the washers, which have a complementary aperture therein, are placed over the stud to compress the blanket and rotated 90.degree. and released whereupon the blanket brings the washer into locking engagement with the stud.
The blanket insulating systems have certain drawbacks. One of them is that the fastening means for securing the blankets in place constitute what is called an exposed system, i.e. the outermost ends of the retaining means are exposed to the heat. This often results in burning off of the retaining means and consequent loosening of the blanket. Another drawback of the blanket system is that the blankets generally are not made in thicknesses in excess of 3 inches. Accordingly, if an insulation depth of several inches is required, i.e. as high as 12 inches, then many blankets must be crisscrossed over one another to acquire the required depth. This is costly and time consuming.
A more recent development in the industry is the utilization of what are known as modular insulation blocks. These blocks generally come in configurations of 1 foot square and can range in depths from 4 to 12 inches. One advantage of the modular blocks is that the required depth can be obtained in the single installation. Additionally, the blocks may be of varying density, i.e. higher density and greater insulating qualities toward the hot face than back toward the cold face.
The modular blocks may be secured to the wall of the furnace or the like in a number of ways. One type of retaining device is a wire retainer that is shaped in an H configuration which has 4 projecting prongs interconnected to a central portion. The central portion has an offset portion which is welded to the cold wall of the furnace. A given modular insulation block is impaled upon a pair of the prongs. Thereafter, a next H configured device is shoved into the opposite wall of the block and welded in place followed by another block being placed upon the opposing projecting pair of prongs. The process is repeated until a plurality of blocks form the modular block wall.
Another method of securing the modular insulation blocks is to utilize a metallic expanded metal backing on the blocks. The blocks are positioned in place against the wall of the furnace with the expanded metal against the furnace wall. Thereafter, a collar stud is pushed through the block into contact with the expanded metal and furnace wall and stud welded to secure the modular block in place. Additionally, self tapping threaded members may be employed which are pushed through the block and drilled and threaded into the wall of the furnace. Thereafter, a washer and nut are placed on the threaded member and tightened against the expanded metal to hold the blocks in place.
The advantages of the modular blocks over the insulation blankets are the ease of assembly and the ability to obtain the required insulation thickness quickly. Additionally, the fastening systems used for the modular blocks are not exposed to the hot face and the likelihood of burnoff of the retaining device is substantially less. However, there are certain drawbacks also. One of the drawbacks is that the modular blocks are subject to a certain amount of shrinkage upon heating. As this shrinkage occurs, the interface between adjacent blocks may open permitting heat to migrate between the blocks with possible damage to the cold face of the furnace. Additionally, this possible opening at the interface of the blocks often permits passage of corrosive vapors and the like to the cold face of the furnace.
There are many applications in the industry wherein the advantages of both the insulating blanket and the modular blocks can be effectively taken advantage of. For example, it would be advantageous to have 1 to 2 layers of insulating blanket crisscrossed covered with a vapor barrier to provide the advantages of total integrity of the system against penetration of heat and vapors through the insulation. At the same time, the advantages of the modular blocks may be had by applying the blocks to the outer surface of the insulation blankets and vapor barrier wherein the modular blocks add the advantage of factory controlled blocks of varying density and the ability to build to the desired thickness quickly, efficiently and inexpensively.
A combination insulation blanket-vapor barrier-modular block system is needed by the industry but has been unobtainable or impractical heretofore. The H anchors heretofore utilized to secure the modular blocks cannot be used with the blanket or vapor barriers inasmuch as the blanket and/or vapor barriers cannot be impaled over the H configured retaining devices.
In a like manner, the stud welding method of securing the insulation blocks in place cannot be used inasmuch as the back surface of the insulation block in such a combination will not be against a metallic cold face of the furnace. Additionally, the self tapping threaded fasteners are not practical since their initial concept of usage is to drill, tap and secure the modular block once the block is in place which does not provide any way of securing the blanket and vapor barrier prior to placing of the blocks. It would be impractical to drill and tap the threaded devices prior to installing of the modular blocks in that alignment and threading of the nut and washers to the device thereafter would require a separate operation and be time consuming and costly.